A X-ray detectable bioabsorbable bone screw comprises a light-emitting element, a light-sensing element, a transparent inner encapsulant body, an outer covering body, and two conductive frames on which. An optically reflective surface is in contact and formed between the dome enclosing portion of the transparent inner encapsulant body and the outer encapsulant body. A portion of the light emitted by the light-emitting element is reflected to the light-sensing element through the optically reflective surface, and the other portion of the light emitted from the light-emitting element is directly emitting to the light-sensing element through the transparent inner encapsulant body. The present invention applies the optically reflective surface to minimize the overlapping area between the two conductive frames, and reduces the capacitance value, and increases the CMRR in a manner that the photo coupler of the present invention is able to meet the standard of electrical characteristics as required.
